The present invention relates to self-healing composite materials.
Thermosetting polymers, used in a wide variety of applications ranging from microelectronics to composite airplane wings, are susceptible to damage in the form of cracking. Often these cracks form deep within the structure where detection is difficult and repair is virtually impossible. In fiber reinforced polymer composites, cracking in the form of fiber-matrix interfacial debonding, ply delamination, and simple matrix cracking leads to degradation. In microelectronics, polymer encapsulates and polymer matrix composite printed circuit boards suffer from similar forms of damage, but in addition to mechanical failure, cracks cause electrical failure of the component. Microcracking induced by thermal and mechanical fatigue is a longstanding problem in polymer adhesives. Regardless of the application, once cracks have formed within polymeric materials, the integrity of the structure is significantly compromised. Typically, previously reported methods of successful crack healing require some form of manual intervention.
A proposed method of self-healing is described in xe2x80x9cSelf-Healing Composites Using Embedded Microspheresxe2x80x9d D. Jung et al. Composites and Functionally Graded Materials vol. MD-80, in Proceedings of the ASME International Mechanical Engineering Conference and Exposition, 265-275 (1997). The proposed method uses polyoxymethyleneurea (PMU) microspheres to store a crack filling agent to be released into the crack and rebond the crack faces. The repair mechanism uses naturally occurring functional sites in a polyester matrix network to trigger the repair action. Adding a reactive component to trigger the crack filler solidification was specifically investigated in the case of embedded epoxide components and embedded amine groups, and it was found that the amine groups did not retain sufficient activity and was determined to be not feasible. The PMU microcapsules used contained an epoxide monomer.
In a first aspect, the present invention is a composite material, containing: a polymer, a polymerizer, a corresponding catalyst for the polymerizer, and a plurality of capsules. The polymerizer is in the capsules.
In a second aspect, the present invention is a composite material, containing: a polymer, a polymerizer, a corresponding activator for the polymerizer, and a first plurality of capsules. The polymerizer is in the capsules, and the corresponding activator is not a native activating moiety.
In a third aspect, the present invention is a method for making the above composites, including dispersing the capsules and the corresponding catalyst or activator into the polymer.
Definitions
A polymerizer is a composition that will form a polymer when it comes into contact with a corresponding activator for the polymerizer. Examples of polymerizers include monomers of polymers such as styrene, ethylene, (meth)acrylates, and dicyclopentadiene (DCPD); a monomer of a multimonomer polymer system such as diols, diamines, and epoxide; and prepolymers such as partially polymerized monomers still capable of further polymerization.
An activator is anything that when contacted or mixed with a polymerizer will form a polymer. Examples of activators are catalysts, initiators, and native activating moieties. A corresponding activator for a polymerizer is an activator that when contacted or mixed with that specific polymerizer will form a polymer.
A catalyst is a compound or moiety that will cause a polymerizable composition to polymerize, and is not always consumed each time it causes polymerization. This is in contrast to initiators and native activating moieties. Examples of catalysts include ring opening polymerization (ROMP) catalysts such as Grubbs catalyst. A corresponding catalyst for a polymerizer is a catalyst that when contacted or mixed with that specific polymerizer will form a polymer.
An initiator is a compound that will cause a polymerizable composition to polymerize, and is always consumed at the time it causes polymerization. Examples of initiators are peroxides (which will form a radical to cause polymerization of an unsaturated monomer); a monomer of a multi-monomer polymer system such as diols, diamines, and epoxide; and amines (which will form a polymer with an epoxide). A corresponding initiator for a polymerizer is an initiator that when contacted or mixed with that specific polymerizer will form a polymer.
A native activating moiety is a moiety of a polymer that when mixed or contacted with a polymerizer will form a polymer, and is always consumed at the time it causes polymerization. Examples of a native activating moiety is an amine moiety (which will form a polymer with an epoxide).
A compound is a molecule that contains at most 100 repeating units. This is in contrast to a polymer, which contains more than 100 repeating units.
A capsule is a hollow closed object having an aspect ratio of 1:1 to 1:10. The aspect ratio of an object is the ratio of the shortest axis to the longest axis; these axes need not be perpendicular. A capsule may have any shape that falls within this aspect ratio, such as a sphere, a toroid, or an irregular ameboid shape. The surface of a capsule may have any texture, for example rough or smooth.